Damping Stopper

ABSTRACT

A damping stopper is interposed between two members axially displaced relative to each other and is provided with an elastic body which, when the interval between the two members decreases, is axially compressed by the two members and expands radially outward. In the elastic body, a second member suppressing the expansion is located in one axial region and attached to the outer periphery. When axially compressed by the two members, the elastic body expands while receiving resistance by the second member. The expanding elastic body contacts the side wall of one of the two members.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. Pat. Application No. 16/767,620filed May 28, 2020, which is a U.S. National Phase application ofInternational Application No. PCT/JP2018/043480, filed on Nov. 27, 2018and published in Japanese as WO2019/116878A1 on Jun. 20, 2019 and claimspriority to Japanese Patent Application No. 2017-240274, filed on Dec.15, 2017. The entire disclosures of the above applications are expresslyincorporated by reference herein.

BACKGROUND Technical Field

The disclosure relates to a damping stopper stopping the displacement ofa movable member, the relative displacement between members, and thelike while exhibiting a damping action.

Related Art

The damping stopper is used as a rack end stopper for an end of asteering rack provided in a steering gear of a vehicle, for example. Asillustrated in FIG. 6 , the rack end stopper compresses and deforms anelastic body 82 containing a rubber material between a rack housing 51and a rack 61 axially facing each other and axially displaced relativeto each other.

A damping stopper 81 damps a shock when the rack 61 collides with therack housing 51 when a steering wheel is vigorously turned to a fulllock in a hydraulically/electrically assisted steering rack, forexample.

The damping of the shock by the damping stopper 81 is performed byabsorbing the kinetic energy by the weight and the speed of a movableobject (rack 61) by the displacement and the reaction force of thedamping stopper 81 (elastic body 82). As illustrated in a graph of FIG.7 , the absorbable energy amount is defined by the size of an area Sillustrated by a diagram obtained by the displacement amount and thereaction force of the damping stopper 81.

Therefore, in order to increase the absorbable energy amount, it iscommon to enlarge the area S by increasing the displacement amount ofthe damping stopper 81 or increasing the reaction force (Rigidity =Spring constant).

The above-described technique has room for improvement in the followingpoints.

The damping stopper 81 requires a proper distortion in order to obtain ahigh reaction force like a nonlinear region as the characteristic of acommon elastic material. In this point, the above-described structurerequires an increase in the stopper size in order to satisfy a requestfunction. However, a design space is limited due to the relationshipwith peripheral components, and thus the size increase is not easy.

As a solution technique for the above-described problem, it isconsidered to obtain a high reaction force by filling, with the elasticbody 82 which is deformed by an input, a clearance c between a matingcomponent (housing 51) and the stopper 81.

However, according to this technique, the reaction force sharply riseswhen the elastic body 82 reaches a filled state, and therefore efficientenergy absorption cannot be performed. As a result, the absorbableenergy amount cannot be increased.

It is an object of the disclosure to provide a damping stopper capableof increasing the absorbable energy amount.

SUMMARY

A damping stopper of the disclosure is provided with an elastic bodyprovided between two members axially displaced relative to each otherand, when the interval between the two members decreases, axiallycompressed by the two members and expanding radially outward and asecond member attached to an outer periphery of the elastic body in oneaxial region of the elastic body and suppressing the expansion of theelastic body in the one region, in which the elastic body expands whilereceiving resistance by the second member to thereby contact a side wallprovided in one member of the two members.

Effect

According to the disclosure, a resistance force by the second member isgenerated in an expansion process of the elastic body, and thus theabsorbable energy amount can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a principal portion of a dampingstopper of a first embodiment.

FIG. 2 is a cross-sectional view of a principal portion illustrating theoperation state of the damping stopper.

FIG. 3 is a graph illustrating the relationship between the displacementamount and the reaction force in the damping stopper.

FIG. 4 is a cross-sectional view of a principal portion of a dampingstopper of a second embodiment.

FIG. 5 is a graph illustrating the relationship between the displacementamount and the reaction force in the damping stopper.

FIG. 6 is a cross-sectional view of a principal portion of a dampingstopper described in the background art.

FIG. 7 is a graph illustrating the relationship between the displacementamount and the reaction force in the damping stopper.

DETAILED DESCRIPTION

A damping stopper 11 of this embodiment is an example of a rack endstopper of a steering rack provided in a steering gear of a vehicle. Asillustrated in FIG. 1 or FIG. 4 , the damping stopper 11 is interposedbetween a rack housing 51 and a rack 61 as two members axially facingeach other and axially displaced relative to each other.

The rack housing 51 has an end surface 52 having a planar shapeperpendicular to the axis. On the outer periphery of the end surface 52,a level difference 53 is provided. On the inner peripheral surface ofthe level difference 53, a side wall 54 is provided. The rack 61 has anend surface 62 axially facing the end surface 52 of the rack housing 51.On the inner periphery of the end surface 62, a level difference 63 isprovided. On the outer peripheral surface of the level difference 63, aside wall 64 is provided. Therefore, an annular mounting space 71, foursides of which are surrounded by the end surface 52 and the side wall 54of the rack housing 51 and the end surface 62 and the side wall 64 ofthe rack 61, is provided. The damping stopper 11 forms an annular shapeas a whole and mounted in the mounting space 71.

First Embodiment

A first embodiment is described based on FIG. 1 to FIG. 3 .

As illustrated in FIG. 1 , the damping stopper 11 has an elastic body 21axially compressed between the end surface 52 of the rack housing 51 andthe end surface 62 of the rack 61.

The elastic body 21 is formed into an annular shape by a predeterminedrubber material. To one axial end (upper side in the figure, the rack 61side) and the inner peripheral surface, a metal attachment ring 31presenting an L-shaped cross section is bonded (vulcanized and bonded).As illustrated in FIG. 2 , when the rack 61 is displaced in thedirection of approaching the rack housing 51 (direction indicated by anarrow D) so that the interval between the end surfaces 52 and 62decreases, the elastic body 21 is axially compressed by the rack housing51 and the rack 61 and expands radially outward.

In the implementation of the disclosure, a metal attachment ring (notillustrated) may be bonded also to the other axial end (lower side inthe figure, the rack housing 51 side) of the elastic body 21.

The damping stopper 11 has a second member 41 attached to one axial partof the outer periphery in the elastic body 21 and restricting theexpansion of the elastic body 21 in the one axial part. Morespecifically, the second member 41 is attached to the outer periphery ofthe elastic body 21 in one axial region of the elastic body 21 andsuppresses the expansion of the elastic body 21 in the one region.

The second member 41 is a ring body having rigidity such that the secondmember 41 does not contact the side wall 54 when the elastic body 21expanding radially outward contacts the side wall 54. The ring body isformed of metal as an example and formed of resin as another example.The ring body has a shape in which the dimension in a directionorthogonal to the axis is larger than the axial dimension and isassembled to an annular mounting groove 24 provided in the elastic body21. The mounting groove 24 is a groove provided beforehand in the outerperipheral surface of the elastic body 21.

The mounting groove 24 is formed at a position where the elastic body 21is divided into a portion 22 of a length L₁ and a portion 23 of a lengthL₂. Therefore, the ring body configuring the second member 41 isattached to a position where the elastic body 21 is divided into theportion 22 of the length L₁ having a long axial length and the portion23 of the length L₂ having a short axial length. It is needless to saythat the axial length does not have an absolutely long-and-shortrelationship and has a relatively long-and-short relationship betweenthe portions 22 and 23. Due to the structure, the ring body has aninterleaf-like shape sandwiched between the portion of the length L₁having a long axial length and the portion of the length L₂ having ashort axial length of the elastic body 21.

As another embodiment, in order to facilitate the assembling work to themounting groove 24, the annular second member 41 may be provided with acut portion or the like in one place on the circumference. Moreover, thesecond member 41 may be buried in the elastic body 21 by carrying outinsert molding in the vulcanization molding of the elastic body 21 by amold. Considering the function or the like thereof, the second member 41is also referred to as a resistance member or also referred to as anelastic body clamping member.

The outer diameter of the second member 41 is formed to be larger thanthe outer diameter of the elastic body 21. Therefore, the second member41 is projected radially outward from the outer peripheral surface ofthe elastic body 21.

The outer diameter of the second member 41 is formed to be smaller thanthe inner diameter of the side wall 54 of the rack housing 51.Therefore, a radial clearance c₁ is formed between the second member 41and the side wall 54. However, the second member 41 does not expand, andtherefore it may be also structured so that the outer diameter of thesecond member 41 is set to be equal to the inner diameter of the sidewall 54 so that the second member 41 is brought into contact with theside wall 54.

The outer diameter of the elastic body 21 is formed to be smaller thanthe inner diameter of the side wall 54 of the rack housing 51, andtherefore radial clearances c₂ are formed between the elastic body 21and the side wall 54.

In the damping stopper 11 of this embodiment, when the rack 61 isdisplaced in the direction of approaching the rack housing 51 (arrow D)so that the interval between the end surfaces 52 and 62 decreases, theelastic body 21 is axially compressed between the rack housing 51 andthe rack 61 and expands radially outward corresponding to thecompression. The second member 41 is attached to one axial part of theouter periphery of the elastic body 21, and therefore acts as aresistance element to the expansion of the elastic body 21. As a result,the radially outward expansion of the elastic body 21 is restricted inthe one axial part.

As described above, the elastic body 21 is divided into the portion 22of the length L₁ having a long axial length and the portion 23 of thelength L₂ having a short axial length. The elastic body 21 expands inboth the portions 22 and 23.

When the portion 22 of the length L₁ having a long axial length and theportion 23 of the length L₂ having a short axial length are compared,the portion 22 of the length L₁ has a surface area larger than that ofthe portion 23 of the length L₂ and more greatly extends radiallyoutward than the portion 23 of the length L₂. As a result, the portion22 of the length L₁ contacts the side wall 54 earlier than the portion23 of the length L₂ as illustrated in FIG. 2 . Then, a situation isrealized in which the portion 23 of the length L₂ does not yet contactthe side wall 54 even when expanding in a state where the portion 22 ofthe length L₁ expands and contacts the side wall 54.

Accordingly, the rise (increase) of the reaction force after the contactbecomes slow as illustrated in a graph of FIG. 3 . Therefore, thedisplacement amount until the allowable reaction force is reachedincreases, and thus efficient energy absorption is enabled and theabsorbable energy amount can be increased.

In the graph of FIG. 3 , Comparative Example illustrates a dampingstopper of a conventional structure not having the second member 41 andthe reaction force sharply rises after contact in Comparative Example,and therefore the displacement amount is small. A point E indicates thetiming when the elastic body 21 contacts the side wall 54.

Second Embodiment

A second embodiment is described based on FIG. 4 and FIG. 5 . The sameportions as those of the first embodiment are designated by the samereference numerals and a description thereof is omitted.

As illustrated in FIG. 4 , a damping stopper 11 has an elastic body 21axially compressed between an end surface 52 of a rack housing 51 and anend surface 62 of a rack 61.

The elastic body 21 is formed into an annular shape by a predeterminedrubber material. To one axial end (upper side in the figure, the rack 61side) and the inner peripheral surface, a metal attachment ring 31presenting an L-shaped cross section is bonded (vulcanized and bonded).When the rack 61 is displaced in the direction of approaching the rackhousing 51 so that the interval between the end surfaces 52 and 62decreases, the elastic body 21 is axially compressed by the rack housing51 and the rack 61 and expands radially outward.

In the implementation of the disclosure, a metal attachment ring (notillustrated) may be bonded also to the other axial end (lower side inthe figure, the rack housing 51 side) of the elastic body 21.

The damping stopper 11 has a second member 41 attached to one axial partof the outer periphery of the elastic body 21 and restricting theexpansion of the elastic body 21 in the one axial part. Morespecifically, the second member 41 is attached to the outer periphery ofthe elastic body 21 in one axial region of the elastic body 21 andsuppresses the expansion of the elastic body 21 in the one region.

The second member 41 is a ring body having elasticity such that thesecond member 41 expands radially outward when pressed by the elasticbody 21 expanding radially outward and rigidity higher than that of theelastic body 21 such that the second member 41 contacts a side wall 54earlier than the elastic body 21. The ring body having such acharacteristic has rigidity higher than that of the elastic body 21 bybeing formed of a material different from that of the elastic body 21.As an example, the second member 41 is formed of urethane.

As another embodiment, in order to facilitate the assembling work to amounting groove 24, the ring body configuring the second member 41 maybe provided with a cut portion in one place on the circumference.Alternatively, the ring body may be divided into two parts on thecircumference to have a halved structure. Considering the function orthe like thereof, the second member 41 is also referred to as aresistance member or also referred to as an elastic body clampingmember.

The outer diameter of the second member 41 is formed to be larger thanthe outer diameter of the elastic body 21. Therefore, the second member41 is projected radially outward from the outer peripheral surface ofthe elastic body 21.

The outer diameter of the second member 41 is formed to be smaller thanthe inner diameter of the side wall 54 of the rack housing 51.Therefore, a radial clearance c₁ is formed between the second member 41and the side wall 54.

The outer diameter of the elastic body 21 is formed to be smaller thanthe inner diameter of the side wall 54 of the rack housing 51.Therefore, radial clearances c₂ are formed between the elastic body 21and the side wall part 54.

In the damping stopper 11 of this embodiment, when the rack 61 isdisplaced in the direction of approaching the rack housing 51 so thatthe interval between the end surfaces 52 and 62 decreases, the elasticbody 21 is axially compressed between the rack housing 51 and the rack61 and expands radially outward corresponding to the compression. Thesecond member 41 is attached to one axial part of the outer periphery ofthe elastic body 21, and therefore acts as a resistance element to theexpansion. As a result, the radially outward expansion of the elasticbody 21 is restricted in the one axial part.

When the elastic body 21 continuously expands in response to a loadaccompanying the displacement of the rack 61, the pressure by theexpansion presses the second member 41 radially outward and expands thesecond member 41 radially outward (diameter enlarging deformation) tobring the second member 41 into contact with the side wall 54. In orderto expand the second member 41 radially outward to bring the secondmember 41 into contact with the side wall 54, a large load is required.Therefore, the rigidity of the entire damping stopper 11 is increased,so that a high reaction force as compared with that in the case wherethe elastic body 21 is used alone is generated

Thereafter, when the rack 61 is displaced in the direction of furtherapproaching the rack housing 51 in the state where the second member 41contacts the side wall 54, the second member 41 slides against the sidewall 54, so that sliding resistance is generated between the secondmember 41 and the side wall 54. The rigidity is increased by the slidingresistance, so that a higher reaction force is generated.

As illustrated in a graph of FIG. 5 , according to the damping stopper11 of this embodiment, a sharp rise (increase) of the reaction force isalready started at the timing (point F) when the second member 41contacts the side wall 54. Thus, efficient energy absorption is enabledand the absorbable energy amount can be increased.

In the graph of FIG. 5 , Comparative Example illustrates thecharacteristic by a damping stopper not having the second member 41. InComparative Example, a sharp rise (increase) of the reaction force isstarted at the timing (point E) where the elastic body 21 contacts theside wall 54. Therefore, efficient energy absorption cannot be performedand the absorbable energy amount cannot be increased.

What is claimed is:
 1. A steering rack assembly, comprising: a steeringrack housing defining a first sidewall and a first end surface thatextends orthogonally outward from the first sidewall; a steering rackthat is axially displaceable relative to the steering rack housing, thesteering rack defining a second sidewall and a second end surface thatextends orthogonally outward from the second sidewall; an annularmounting space positioned between the steering rack housing and thesteering rack, and defined by the first sidewall, the second sidewall,the first end surface, and the second end surface; and a steering rackdamper positioned in the annular mounting space, wherein the steeringrack damper includes: an attachment ring including a first leg that isattached to and extends along the second end surface and a second legthat is attached to and extends along the second sidewall; an elasticbody attached to the attachment ring, the elastic body including a firstaxially extending surface that is attached the second leg and anopposite second axially extending surface that faces and is spaced apartfrom the first sidewall of the steering rack housing, the oppositesecond axially extending surface defining a mounting groove thatseparates the opposite second axially extending surface into a firstportion have a first axial length and a second portion having a secondaxial length that is less than the first axial length, and the elasticbody being configured to be axially compressed by the steering rack andthe steering rack housing as the steering rack is axially displacedrelative to the steering rack housing; and a rigid ring located in themounting groove of the elastic body and spaced apart from the firstsidewall of the steering rack housing, wherein as the elastic body isaxially compressed as the steering rack is axially displaced relative tothe steering rack housing, the rigid ring suppresses outward expansionof the elastic body such that the first portion of the opposite secondaxially extending surface expands outward and contacts the firstsidewall and the second portion of the opposite second axially extendingsurface expands outward without contacting the first sidewall.
 2. Thesteering rack assembly according to claim 1, wherein the rigid ring islocated in the mounting groove such that the rigid ring is always spacedapart from the first sidewall.
 3. The steering rack assembly accordingto claim 1, wherein the rigid ring is formed of a metal material or apolymeric material.
 4. The steering rack assembly according to claim 1,wherein a radial length of the rigid ring is greater than an axiallength of the rigid ring.
 5. The steering rack assembly according toclaim 1, wherein an inner wall of the mounting groove is positionednearer to the first axially extending surface of the elastic body incomparison to the second axially extending surface of the elastic body.6. The steering rack assembly according to claim 1, wherein the rigidring is configured to suppress outward expansion of the elastic bodysuch that axial compression of the elastic body is increased to increasean amount of energy absorbed by the elastic body as the steering rack isaxially displaced relative to the steering rack housing.
 7. The steeringrack assembly according to claim 1, wherein the rigid ring is buried inthe elastic body.